Fluid system control



March 14, 1944. DAVIS, JR 2,344,133

FLUID SYSTEM CONTROL Filed June 9, 1941 2 Sheets-Sheet 1 INVENTOR:ARCHIBALD H. DAVIS JR.

ATTORNEYS,

Fl G.

March 1944- A. H. DAVIS, JR 2,344,133

FLUID SYSTEM CONTROL Filed June 9, 1941 2 Sheets-Sheet 2 &

l 6- 5 I I INVENTOR:

ARCHIBALD H. VIS JR.

ATTORNEYS.

Patented Mar. 14, 1944 FLUID SYSTEM CONTROL Archibald B. Davis, Jr.,Moline, Ill., assignor to American Machine and Metals, Inc., New York,N. Y., a corporation of Delaware Application June 9, 1941, Serial No.397,170

7 Claims.

This invention relates to hydraulic driven testing apparatus in whichthe movable platen is to move toward or away from a fixed head at auniform rate.

This requires that the rate of motion of the ram be uniform withincloser limits than is required in most other hydraulic equipment. Thisuniformity of motion must be maintained even though the resistance ofthe specimen and the load on the machine vary sharply.

Though the invention is primarily applicable to universal testingmachines the invention is not limited thereto but includes all hydraulicplunger applications in which uniformity of motion is to be seemeddespite variable resistance.

In the practice of this invention a cylinder is provided with a meteringfeed device giving a constant rate of liquid feed and a secondary supplyfrom which measured additional liquid may be discharged into the systemdepending upon the load on the machine and the position of the ram inthe cylinder.

The additional liquid may be discharged into the cylinder manually or,preferably, automatically as the pressure rises.

The amount discharged may be made to vary not only with the pressurechange of the liquid but also with the amount of oil already in thecylinder of the testing machine.

At the beginning of the stroke, before the specimen creates muchresistance, the pressure on the ram, and therefore the pressure on theoil, that is fed to the cylinder is low. As the resistance of thespecimen increases, so will the pressure on the oil, and in commercialpractice this pressure may rise to 3000# per square inch or more.

Various devices have been provided, the object of which is to feed theliquid, usually oil, at a constant metered rate regardless of thecounter pressure of the ram. Applicant's earlier application on a Fluidsystem control filed March 22, 1941, Serial No. 384,692, shows such acontrol designed to feed liquid to the cylinder at a uniform rate.

Tests with machines equipped with metering controls that feed the oil atan absolutely uniform rate show that the rate of feed of the tabledecreases as the load is applied. The reason for this is that when theram moves forward under low pressure, the space underneath the rain hasbeen filled with oil at low pressure. Even though, under the increasedresistance, the metering device delivers additional 011 alreadycompressed at the same rate as before some of that oil will be used tomake up for the reduction in volume of theoil already in the cylinderdue to the compression of the oil under the wide range of pressure used.

The tests have shown that, to secure uniform motion of the ram we mustfeed at a faster rate than normal when the pressure in the system isrising and at a slower rate than normal if the pressure is falling.

- In a standard universal testing machine, with a piston elevated 6"from the bottom of the cylinder. the volume of oil required to compressthe 300 cubic inches of oil under the piston to 3000# is approximately.33 cubic inch. This means that with an oil feed of .50 cubic inch perminute (corresponding to .01" per minute desired feed), and a pecimenthat loads the machine to full rating in one minute the .50 cubic inchof oil is divided into .33 cubic inch for compression of oil and .17cubic inch for movement of the piston. The feed would be only.17/50:.0034" per minute instead of the .01 feed desired.

The difliculty cannot be eliminated by recalibrating the metering systemso that an opening of the control valve that is marked .010'. per minuteactually passes oil enough to both cover that movement and to offset oilcompression.

For if the next specimen loaded itself in two minutes instead of oneminute th oil compression would be overcorrected, and if it took tenminutes the necessary correction would be only .033 cubic inch perminute so that one valve, for the same setting, would give us a feed of.010" for a one-minute loading and .016" per minute for a two-minuteloading time.

The invention provides a second supply of liquid from which enough isdischarged into the already metered supply to the cylinder to make upfor the compression of the oil previously fed to the cylinder at thelower pressures.

This recognizes that the additional amount of oil is a function of thecompressibility of the oil, of the volume of oil under the plunger atthe time the test is to be made, and of the rise of pressure during thetest.

The device may be manually operated at the right time or it may be madeto automatically discharge the proper amount of oil into the cylinder asthe pressure rises.

The object of the invention is to provide a universal testing machine orthe like in which A further object is to provide a supplementary storagereservoir from which an amount of liquid approximately equal to thatneeded to offset the compression of the oil is automatically dischargedinto the cylinder.

A further object is to provide a device which will automatically correctfor the compression of oil in the ram of the testing machine taking intoaccount both the rate of change in pressure and the volume of the oil inthe cylinder at the working range.

This compensator is intended for use in connection with a precalibratedrate of oil feed. If we had a slow speed and a uniform load over widerange, such as an extruding operation, the precalibrated speed would bemaintained and require no correction. However, when, as in normaltesting operations, the early portion of the stroke is merely to take upslack and apply the initial load and then the pressure rises up to theend of the test, the precalibrated speed will not be maintained duringthe latter, and the important part of the test, because some of the, oilbeing supplied instead of being used to move the ram is used to make upfor the compression of the oil which has already been supplied.

Figure 1 is a diagrammatic arrangement, partly in section, of auniversal hydraulic testing machine equipped with a control constructedas disclosed in the above cited prior application and with theadditional oil compression compensator which is the subject of thisinvention.

Figure 2 is an enlarged elevation, partly in section, of the oilcompensator.

Figure 3 is a section of the compensator taken along line 3-3 of Figure2.

The invention comprises a source of power generally indicated at I, apump generally indicated at 6, drawing liquid from a reservoir 8, andfeeding through the device 23 designed to give a uniform flow for anygiven setting of the valve 52 to the cylinder of the machine generallyindicated at 20. The machine is equipped with means for preventingleakage along the cylinder walls which do not impose frictionalresistance in the manner explained in applicants earlier application,Serial No. 334,333, filed May 10, 1940. This fluid packing is appliedthrough the groove generally indicated at H. The plunger I9 of thetesting machine exerts pressure upon a specimen 50 in a universalmachine of conventional type I00.

A cylinder generally indicated as MI in Figure 2 contains liquid, whichmay be discharged through line I04 when the pressure under the ramovercomes a calibrated spring I20. This amount also takes into accountthe height to which the plunger has moved. This is accomplished bymanually setting handle I35 in proper relation to scale I40.

When the test is completed and the pressure is released the spring I20will automatically refill cylinder |I preparatory to the next test to beperformed.

I is normally a motor shaft driving a multi-. cylinder plunger pump 0which draws liquid in through a check valve 1 and discharges through acheck valve I2 liquid drawn from reservoir I into line I3. It isunderstood that oil under adequate pressure and in adequate volume maybe supplied to main I2 in any manner desired as the pump does not formany part'of the invention. Liquid under pressure is supplied throughlines I4 and I0 to the fluid packing groove I1 .I28 slides along armI35.

referred to in the previous application on fluid packing.

Liquid under pressure is also supplied through line I5 to a pressurecontroller generally indicated at 22 which provides a uniform pressuredifferential across the manually adjustable controller valve 52 whichfeeds into a. line 55 to space 20 in cylinder I8. The construction ofthis pressure reducer is shown in detail in Figure 1 of the fluidcontrol application #384,692, previously referred to. The uniformpressure differential across valve 52 is obtained by controlling thedischarge through bypass 42 which reduces the pump pressure to apredetermined amount above the pressure in line 55. This control isautomatically accomplished by the pressure control at 22. The dischargedoil passes into line 22 which collects the leakage from groove H anddischarges through I0 into tank 0.

Summarizing, the pressure in lines I4, I5, I5, and fluid packing grooveI! will always be slightly above the pressure in line 55 and space 20.This amount will be just suflicient to give the desired rate of uniformdischarge across the contraction imposed at valve 52. Through line I02which connects with feed line I5, space 98 below the piston is under thesame pressure as the supply side of valve 52. Normally this piston is inthe position shown resting upon the piston extension 95. The upper sideof this piston, space 91, discharges through line I04 into line 55.Accordingly, whenever piston I02 moves upwards a quantity of oilproportional to the amount of movement of piston I02 is dischargedthrough line I04 into 55. This is in addition to that supplied throughthe metering valve 52.

The unit pressure on the under side of the piston I02 is higher than theunit pressure on the upper side of the piston. Also the area of theupper side is smaller than the area of the lower side by the area ofstem I08. Accordingly there will be a differential pressure tending tomove piston I02 and its stem I08 upwards. This is resisted by pad II8 ofa swinging lever II5 which is pivoted at I I1.

This frame carries a slot II5, substantially an arc concentric withpivot I30 when the pad III is in its lowest position. On pivot I30 anarm I35 may be swung by handle I30. A carriage It carries a roller I25on a stud N9, the roller traveling in the 'arcuate sIOtIIB of lever H5.The carriage I20 is urged toward pivot I30 by a calibrated spring I28which engages the carriage at I21 and the end piece of the lever, I29,at I3I. This spring is selected of such length and such resistance toelongate as is required. The initial stress will Just offset theunbalance of forces on piston I02, just described, tending to lift thepiston before load is applied.

Assume that the lever I25 has been swung to the extreme left'and theplunger I5 is at the bottom of the cylinder. The end of the lever movesalong an arcuat scale I40 which is fastened by screws I4I to studs I42upon the panel generally indicated at 09. The spring, which is shown ofa fixed length but one end of which may be fastened adjustably to permitvarying its effective length is under a tension Just sufficient toprevent the rise of plunger I08 when the pressure under the ram of themachine is merely that corresponding to the weight of the table and itsaccessories being lifted. There will be no discharge from space 01 intoline I04. As the testing proceeds and the ram meets rei 2,s44,1as

sistance the pressure in line I04 will increase and the pressure in I03will increase correspondingly. The diflerence between the unit pressureson the two sides or the piston has already been counterbalanced by theinitial tension of spring I28. The increased pressure in line I03 actingover the difference in area between the two sides of the piston is notcounterbalanced however and therefore the piston I02 will rise, somewhatincreasing the tension on spring I08. This small movement of plunger I02has discharged a small quantity of oil through line I04 to oil'set thecompression of the oil already in the cylinder by the increased pressureat which the oil is now being delivered to the cylinder. It will be seenthat the amount liquid discharged from space 01 is directly proportionalto the increased pressure in the cylinder.

The purpose of lever I35 permitting the movement of roller I I5 in slotH6 is to give an increased movement to pad II! and therefore anincreased movement of plunger I02 for a given pressure in the cylinder,it-desired, by moving the handle I36 a small distance to the right. Thusthe amount of oil discharged can be increased and we can determineexperimentally the point of the end of the lever on the scale I40 thatwill correct for the compression of th 011, not only in the cylinder butin the piping system when the piston I9 is at the bottom. It is clearthat it the piston is part way up there will be more oil under thepiston, more oil required to make the compressibility correction.Accordingly lever I35 will be moved further to the right to a point onthe scale I40 which may be experimentally determined that will give theincreased discharge of oil through I04 to make the correction.

In the arrangement shown in the drawing it is necessary to manually movelever I35 by scale I40 to correspond to the position of platen I50 asindicated by pointer I5I on vertical scale I52.

Since the position of lever I35 is related to the position 02! platenI50 on top of piston I9 it may be moved thereby by the use of a,suitable system of levers and connecting rods so that the position oflever I35 will automatically correspond to the position of the platen.

In the ordinary test where the position of the piston corresponds to theadjustment oi the platen to the specimen length, and the actual testextends over only a short vertical range, this procedure may besimplified by moving the lever I35 but once to the positioncorresponding to that at which the actual test load is applied.

If however the load increases over a considerable range of the stroke ofplunger I 3 lever I35 should b moved over the corresponding range of thescale in the same manner as it would had it been connected mechanicallyto the platen.

When the loadis released from the specimen and the pressure in line I04drops the extended spring I28 will automatically restore the parts tothe condition shown in Figure 2 and therefore space 91 will draw in thesame amount of oil discharged duringthe load application. Thus, at thebeginning of each new test piston I02 is always in its lower position asshown. The device 50# per square inch, and the loss of liquid in a wellfitted piston and plunger under such low pressure diflerential isnegligible. Line I05 and groove I 06 form a fluid packing of the sametype shown in the earlier application and the loss of oil due to thehigh pressure drop between grooves I00 and I0! represents only thereturn of an indefinite and unimportant quantity of liquid from theunmetered supply line I05 through I01 back to the sump.

It will be understood that the parts are so designed that when theplunger of the testing machine is at maximum load and at maximum strokeand lever I35 moves toward the right the movement of piston 102 will notquite equal the length of stroke permitted by cylinder I M and that forall other conditions of testing the stroke of piston I02 will be less.

I claim:

1. A hydraulic system comprising; in combination, a source of liquidsupply, a pressure chamber, a conduit leading from the source of supplyto the pressure chamber, a metering device in said conduit, a liquidcontainer for adding additional liquid to the pressure chamber to offsetthe loss of volume of liquid in the chamber when the pressure increases,the container including a difl'erential piston, a connection from thesource of pressure to one end of the container tending to drive thedifierential piston forward, a connection from the opposite side of thedifl'erentiai piston leading from the container to the chamber and meansoffering increasing resistance to the movement of the difierentialpiston so that the volume of liquid ejected corresponds to the movementof the differential piston and the change of pressure in the system.

2. In combination, a cylinder, a plunger movable therein, a source ofsupply of fluid under pressure, a conduit leading from the fluid supplyto the cylinder, a metering valve in the conduit, a pressure controllerahead of the metering valve, a discharge opening in the conduitcontherefore corrects for the decompression of the oil as pressure isreleased, for instance, because of passing the elastic limit of thespecimen, as well as for the compression as pressure is increased.

It will be evident that in attempting to correct for inaccuracies of theorder of a fraction of a cubic inch or fluid there must be no leakagewithtrolled by the pressure controller for diverting a part of the fluidsupply, the pressure controller being adapted to maintain a constantdifferential across the metering valve by varying the proportion oi. thefluid supply that is diverted; a supply chamber ror additional fluid, afloating piston therein, a connection from one side of the meteringvalve to one end of the supply chamber, a connection from the other sideof the metering valve to the other side of the supply chamber, a springstressed by the movement of the piston in the chamber, the springpermitting further movement of the piston and further discharge ofadditional fluid into the cylinder only as the pressure on one side ofthe metering valve increases.

3. A hydraulic system comprising, in combination, an expansible chamber,a source of liquid under pressure, a conduit leading from the source tothe chamber, a metering device in said conduit, means for compensatingfor the change of volume of the liquid already metered due to changes inthe pressure on the liquid in the chamber by adding or withdrawing ameasured quantity of additional liquid to the chamber comprising a inthe correcting device. Accordingly, to prevent tank, a diflerentialpiston therein, conduits connecting one side of the piston to one sideor the metering device and the other side oi the piston 'to the otherside of the metering device, the pressures upon the diilerential pistonareas creating a force that varies with the pressure in the chamher andtends to move the piston, means including'a spring progressivelystressed as the piston tion, an expansible chamber, a source of liquidunder pressure, a conduit from the source to the chamber, a meteringdevice in said conduit, means for compensating for the change of volumeof the liquid already metered due to changes under pressure, a conduitfrom the source to the chamber, a meterinr device in said conduit,

, means for compensating for the change 01 volume oi. the liquid alreadymetered due to changes in the pressure of the liquid in the chamber byadding or withdrawing a measured quantity of additional liquid ,to thechamber comprising, a

- tank of liquid, a diflerential piston therein, conin the pressure ofthe liquid in the chamber by adding. or withdrawing a measured quantityof additional liquid to thelcham-ber comprising a tank of liquid, adifferential piston therein, conduits connecting one side of the pistonto one side of the meter and the other side of the piston to the otherside of the meter, the pressures upon the diflerential piston areascreating a force that varies with the pressure in the chamber, a base onwhich the tank is mounted, a lever pivoted on the base, one end bearingagainst the piston, a cam surface on the lever, an arm pivoted on thebase, a slider bearing on the cam that is free to move along the arm, aspring "urging the slider against the cam and thereby exerting pressureon the plunger whereby the quantity of fluid delivered from the tank fora given pressure change in the chamber can 'be varied by setting thearm.

5. A- hydraulic system comprising, in combination, an expansiblechamber, a source of liquid duits connecting one side oi! the pistonjroone side of the meter and the other side 0! the piston to the other sideof .the meter, the pressures upon the differential piston areas creatinga force that varies with the pressure in the chamber, a base on whichthe tank is mounted, a lever pivoted on the base, one end bearingagainst the piston, a cam surface on the lever, an arm pivoted on thebase, a slider bearing on the cam that is free to move along the arm, aspring urging the slider against the cam and thereby exerting pressureon the plunger, a scale on the base over which the arm moves calibratedfor the approximate volume or the chamber in use whereby the quantity offluid delivered from the tank for a given pressure change in the chambercan be varied according to the size of the expansi-ble chamber bysetting the arm.

